A new method for the heliostat field optimization is presented. The method is intended for further performance improvement after initial layout with a standard heliostat field layout tool. During the field refinement, the heliostats are repositioned around their original position, without or with little restrictions. A nonsimplifying ray-tracing tool is used for the performance evaluation. During the optimization, detailed local weather and site characteristics (e.g., topography) can be considered. An example case is presented and discussed. This case is based on a field layout for a plant similar to the PS10 solar tower plant in Spain. In this case, an improvement of the annual intercepted energy into the receiver of about 0.8% was achieved, by slightly repositioning the heliostats. Application of the refinement method is recommended for any future solar tower plant. Basically, the optimization improves the revenues while capital and O&M cost remain unchanged. It is expected that any standard heliostat layout can be improved to a certain degree using this method. The method is very flexible and can be easily adapted to specific situations and optimization goals.